1. Field of the Invention
The present invention is directed to an electrostatic relay driven by an electrostatic force to open and close a contact.
2. Description of the Related Art
Electrostatic relays are known in the art, for example, as disclosed in U.S. Pat. No. 4,078,183 and Japanese Patent Early Publication (KOKAI) No. 2-100224. The electrostatic relay of U.S. Pat. No. 4,078,183 comprises a pair of parallel fixed electrodes and a movable electret which is disposed between the fixed electrodes and is supported at one end to a common base to the fixed electrodes. The movable electret carries a movable contact at the other end which is made movable toward and against the adjacent portions of the fixed electrodes for closing and opening the movable contacts to and from associated fixed contacts on the fixed electrodes. The movable electret is charged to have different electric charges from one side to the other side of the electret so that, when no control voltage is applied across the fixed electrodes, the movable electret is kept attracted to one of the fixed electrodes to close the movable contact to the associated fixed contact on the fixed electrode. When a control voltage of a given polarity is applied across the fixed electrodes, the electret is attracted toward the other fixed electrode to open the contacts. In the relay of this patent, the movable electret extends generally in parallel with the fixed electrodes, particularly at one end portion at which the electret is supported to the common base such that a gap of substantially constant width remains between the supporting end of the movable electret and the adjacent fixed electrodes. With this gap of substantially constant width, a relatively large electric potential is required to move the contact end of the electret between the fixed electrodes by electrostatic force for closing and opening the contacts. Therefore, there remains a certain limitation in obtaining a large electrostatic force enough to move the movable electret between the fixed electrodes for closing and opening the contacts with a less electric potential applied across the fixed electrodes. With this result, it is also difficult to obtain a sufficient contacting pressure with a small electric potential applied across the fixed electrodes.
The electrostatic relay of Japanese patent No. 2-100224 comprises a base mounting thereon a pair of fixed electrodes and an actuator frame superimposed on the base. The actuator frame defines therein a pair of movable electrodes each in the form of a flap supporting at its one end to the frame and extending along the adjacent fixed electrode. The movable electrode is allowed to pivot about the supporting end for closing and opening a movable contact on the free end of the movable electrode to and from associated fixed contacts on the base. An external control voltage source is connected to apply a potential difference across the fixed electrode and the movable electrode to generate an electrostatic force between the movable electrode and the associated fixed electrode, whereby attracting the movable electrode toward the base for closing the contacts. Upon no electric potential being applied between the movable electrode and the fixed electrodes, the movable electrode returns to a neutral position of opening the contacts by inherent resiliency given to the movable electrode. Also in this relay, the movable electrode extends generally in parallel with the adjacent fixed electrode to leave a gap of constant width along the movable electrode when no electric potential is applied across the movable electrode and the fixed electrode. Therefore, this relay suffers also from the limitation in that a electrostatic force large enough to attract the movable electrode towards the fixed electrode for closing the contacts is difficult to obtain with a small applied electric potential. Therefore, it is likewise difficult to obtain a sufficient contacting pressure with a small applied electric potential.